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Abstract

Semiconductor quantum dots (QDs) are brightly luminescent nanoparticles that
have found numerous applications in bioanalysis and bioimaging. In this review, we
highlight recent developments in these areas in the context of specific methods for
fluorescence spectroscopy and imaging. Following a primer on the structure,
properties, and biofunctionalization of QDs, we describe select examples of how QDs
have been used in combination with steady-state or time-resolved spectroscopic
techniques to develop a variety of assays, bioprobes, and biosensors that function
via changes in QD photoluminescence intensity, polarization, or lifetime. Some
special attention is paid to the use of Förster resonance energy transfer-type
methods in bioanalysis, including those based on bioluminescence and
chemiluminescence. Direct chemiluminescence, electrochemiluminescence, and charge
transfer quenching are similarly discussed. We further describe the combination of
QDs and flow cytometry, including traditional cellular analyses and spectrally
encoded barcode-based assay technologies, before turning our attention to enhanced
fluorescence techniques based on photonic crystals or plasmon coupling. Finally, we
survey the use of QDs across different platforms for biological fluorescence
imaging, including epifluorescence, confocal, and two-photon excitation microscopy;
single particle tracking and fluorescence correlation spectroscopy; super-resolution
imaging; near-field scanning optical microscopy; and fluorescence lifetime imaging
microscopy. In each of the above-mentioned platforms, QDs provide the brightness
needed for highly sensitive detection, the photostability needed for tracking
dynamic processes, or the multiplexing capacity needed to elucidate complex systems.
There is a clear synergy between advances in QD materials and spectroscopy and
imaging techniques, as both must be applied in concert to achieve their full
potential.